When we asked you to nominate some intellectual cliches for this series earlier this year, Adam Smith's "invisible hand" cropped up repeatedly, with mentions by Comment is free regulars steffanjohn, JonathanKent and TimWorstall – and PatDavers claiming that "we'd have hours of fun with that one". Well, let the fun commence.

In the third episode of The Big Ideas, Benjamen Walker discusses the meaning and uses of Smith's concept with philosopher John Gray, academic Marianne Johnson, economist Eamonn Butler and Guardian columnist Polly Toynbee. We'll be following up the podcast over the course of this and next week with a series of articles looking at Smith's idea from different perspectives.

As we mention in the podcast, Smith himself only used the phrase "invisible hand" sparingly. It crops up for the first time in part IV of the first chapter of Theory of Moral Sentiments (1759):

The proud and unfeeling landlord views his extensive fields, and without a thought for the wants of his brethren, in imagination consumes himself the whole harvest … [Yet] the capacity of his stomach bears no proportion to the immensity of his desires..the rest he will be obliged to distribute among those, who prepare, in the nicest manner, that little which he himself makes use of, among those who fit up the palace in which this little is to be consumed, among those who provide and keep in order all the different baubles and trinkets which are employed in the economy of greatness; all of whom thus derive from his luxury and caprice, that share of the necessaries of life, which they would in vain have expected from his humanity or his justice … The rich … are led by an invisible hand to make nearly the same distribution of the necessaries of life, which would have been made, had the earth been divided into equal portions among all its inhabitants, and thus without intending it, without knowing it, advance the interest of the society …

The second mention is in book one, chapter seven, of The Wealth of Nations (1776):

By preferring the support of domestic to that of foreign industry, he intends only his own security; and by directing that industry in such a manner as its produce may be of the greatest value, he intends only his own gain, and he is in this, as in many other cases, led by an invisible hand to promote an end which was no part of his intention. Nor is it always the worse for the society that it was not part of it. By pursuing his own interest he frequently promotes that of the society more effectually than when he really intends to promote it. I have never known much good done by those who affected to trade for the public good. It is an affectation, indeed, not very common among merchants, and very few words need be employed in dissuading them from it.

So what is the "invisible hand"? Is it a sound economic principle grounded in scientific fact? Or is it a nebulous myth? One thing is sure: with stockmarkets tumbling and global economics in permanent crisis, Smith's concept continues to be one of the most controversial big ideas around.

Adam Smith portrait on the new twenty pound note.
Photograph: David Levene for the Guardian